Electric furnace



Aug. 9, 1938. P. B. CROCKER ELECTRIC FURNACE Filed Nov. 5; 1955 3 Sheets-Sheet 1 Grow @3 1; 7 714 17 Aug. 9, 1938. P. B. CROCKER 2,126,454

ELECTRIC FURNACE Filed Nov. 5. 1935 -3 Sheets-Sheet 2 Z w, w //f///// 4 a W? 7 a nwm I ma Tw P I: m. wy 1 v 14 fiM Wfi "w u nw fu lifi uk/ fiMumw/"v/ J flfi Wfl i w 7 7 "u (0 9% 5 C a x a Q a a e C. A 1 7 3 3 4/ fl 4 P. B. CROCKER 2,126,454

ELECTRIC FURNACE Filed Nov. 5, 1935 3 Sheets-Sheet 3 8'9 Invezaior:

Patented Aug. 91, 1938 t I I I i UNIT D STATES PATENT OFFICE, mafiifima Percival B. Crocker; Foxboro, Mass, assignor to The Sentry Company, Foxboro, Mass, a corporation of-Massachusetts Application November 5, 1935, Serial No. 4 .326 10 Claims. (01. 13-20) This invention relates to electric furnaces of provided with suitable openings 21 to receive the the type utilizing resistors such as rodsof silicon ends of resistor rods 29 of silicon carbide or the carbide or the like, and the object is to provide like. I have herein shown four such I certain improvements in such furnaces faciliposed in a generally quadrate arrangement. At

5 tating their construction and promoting efficiency the location of these openings 21 the blocks l9 5 and convenience in use. Electric furnaces of the reach substantially to the inner wall of the casing type referred to find an extensive application in or shell 1 but are cut away around the openings hardening high speed steel, in which case it is to provide for the interposition of heat insulatdesirable to provide for continual operation at ing Packing 23a in the er S own in F 4 10 temperatures of substantially 2300 F. This and and 5, the construction being such that each 10 higher temperatures are also used for many opening 21 comes to the outer side of the block ceramic operations. The particular design of through a projection or raised portion of somefurnace which is here illustrated as an example what frusto-conical form. I also prefer to pmof my invention is designed for operation under vide between these projections through which the such conditions and, among other things, pro- Op extend a centrally disposed raised D 15 vides in a construction of simple form for a. tion 31 extending substantially to the plane of proper cooling of the terminals whil minimizing the inner wall of the shell, as best shown in Fig. 5, heat losses. for a purpose to be described. To support the My invention willbe well understood by refershell of the casing n al nme t w th the side wall ence to the following description of the illustraand prevent its warping, the portion thereof fac- 20 tive embodiment thereof shown by way of example g e side wall is Preferably lined W 8 Sheet in the accompanying drawings, wherein:- of asbestos board 33.

Fig. 1 is a front elevation of the furnace; Current is supplied to the resistors 29 through Fig. 2 is a longitudinal section on the line 2-2 terminals 35 and 31 engaging the ends thereof of Fig. 1; respectively within the openings 21, the terminals 25 Figs. 3 and 4 are vertical sections on the lines extending outwardly beyond the shell of the fur- 3-3 and 4'-4 of Fig, 2, respectively; I nace'chamber for air cooling, being here shown Fig. 5 is a plan section on the line 5-5 of as provided with heat radiating fins. These Fig. 4; terminals provide for connecting the resistors Fig. 6 is an enlarged fragmentary sectional together and to a source of electrical energy in a 30 detail of'the part shown in Fig. 5; and manner e e ary. to describe in detail, the

Fig. '7 is a section on the line 1-1 of Fig.-3. connection usually being in series. The furnace herein shown comprises essentially To protect the terminals and their connections a chamber for receiving the work having walls of I provide shielding plates 39 and 4| in spaced suitable refractory material and adapted to be relation to the side walls of the furnace chamber. 35 heated internally by electric resistors. This ese Plates y consist sbe to board o chamber or enclosure is herein organized in a like non-conducting material and are herein metallic casing comprising a shell 1 encircling shown as Su p v n n rel t fr m the lateralqwalls and top and bottom plates 9 the sides of the chamber by means of suitable 40 and ii which may be secured thereto through spacers 43 and 45.

angles 13. Received'within this shell isa bottom Referring to Fig. 4, the right-hand terminal 35 wall IS, a rear wall 11, side' walls It and a is there shown as abutting the inner surface of roof 2| supported from the side walls, all formed plate 39 whichis provided with a recess 41 to from suitable refractory blocks or shapes, the receive a stud-like projection 48 on the endof the side walls is conveniently being each formed as 1 terminal. The other plate isprovided with 45 here shown from a single block of specialform suitable openings II in alignment with the openas hereinafter more fully described. The rear and lugs 21 in the side walls of the furnace chamber. top walls may be'spaced from the adjacent walls Through these openings ii the resistor rods 29 of the casing and are covered by heat-insulating and the left-hand terminal 31 may be inserted 50 packing material 23 interposed between the same into the position shown. Each pair of opposing 50 and the casing. As indicated in Fig. 5, the rear terminals" is held between the end plates, suswall l1 may be provided with the opening 25 for pending the resistor 2 between them, by an the insertion of athermc-couple. end thrust between the plates which may be Referring more particularly to Fig. 4, the greefiected by suitable spring means acting on ters5 fractory blocks II which form the side walls are minal 31? I have herein shown blade springs 53 5 secured to the shielding plate 4| and adapted to be swung into position over the openings II to engage under tension the ends of terminals 31. These terminals may be provided with buttonlike insulators II at their ends against which the springs bear. This arrangement with the springs as a whole insulated from the electric heating circult is a most convenient and desirable one.

The description so far has been somewhat didactic. An understanding of the construction described may perhaps be facilitated by a further discussion at this point. In a furnace of the present kind the conditions as to heat conduction and insulation are somewhat paradoxical. The furnace shown, for example, is one designed for continued operation at temperatures at substantially 2300" R, which is approximately the conventional temperature for hardening high speed steel. Loss of heat from the working chamber is, of course, to be avoided. On the other hand, the terminals which support the resistors must be adequately cooled to prevent their rapid corrosion and failure. Herein the resistor rods 29 are shown as extending substantially to the exterior of the side wall I! and the openings 21 thereabout are flared inwardly. It

, will be understood that all parts of the resistor generate heat and by this arrangement reflection of heat from the walls of the opening into the chamber and radiation and convection from about the ends of the resistors to the heating chamber is facilitated. At the same time the ends of the terminals I! and 31 extend very slightly within the wall and are thus not unduly pocketed within a highly heated opening. The side walls l9 are constructed of flrebrick or some like material not of high heat-insulating value. Consequently the elevated portions of the exterior face of the walls surrounding the openings 21 and extending to the casing provide a path for heat dissipation by conduction from the inner ends of the terminals while the distance to the fully exposed air-cooled portions thereof is short. At the parts of the sides of the furnace structure relatively remote from the positions of the terminals, the relatively eflicient heat insulating material 23 and 23a minimizes heat loss.

To avail of this balanced construction whereby a heat loss at the point of contact between the terminals and the resistor rod is permitted. while practically the entire length of the resistor rod is utilized for useful heating purposes, the wall I! may be relatively thin. The length of the flared opening surrounding the end of the resistor rod is thus short. To minimize the loss of heat from the interior chamber of the furnace while availing of the convenient construction within the metal case ll and without interfering with the necessary heat loss at the terminals or their efficient cooling by air, I provide an additional thickness of insulating material in alignment with the side walls of the interior heated chamber in the form of blocks 51 interposed between the side walls and the shields ll and II, these blocks herein bearing on the elevated portion ll of side wall block I! hereinbefore referred to. These blocks I! thus overlie the relatively thin wall I! opposite the center of the heating chamber and, the resistor rods 20 being located in the corners of the heating chamber, the blocks I! are received within the groups of terminals II and I1 and minimize the loss of heat from the central chamber while permitting both the radiation fromthepointsofcontactoftheterminals' and the resistor bars and the free circulation of air about the terminals to cool the same. As best seen in- Fig. 5, to facilitate the cooling of the terminals the blocks 51 may be somewhat tapered outwardly as shown.

Referring now more particularly to Figs. 2, 3 and 7, the front of the furnace chamber may be closed in part by a throat, herein formed of a silllike slab 6|, slabs 63 forming the jambs of the opening and having rabbets 6| extending along the upper portions of their inner edge and a lintel-like slab 65 having flanges 68 received in the rabbet 64 and engaging the shoulder thereof. The jambs 63 and the lintel piece 65 deflne an opening giving access to the heating chamber. Suitable means are provided for receiving the work, which work-receiving means is herein exemplified as a muflle 81 extending within the furnace and having an open end received in said opening, the top and side edges of the muilies being provided with flanges 69 entering rabbets II in the slabs 63 and 65. The further end of the muiiie 61 may be supported on a projecting end 13 of one of the blocks of the back wall.

Exteriorly of the throat formed by the slabs referred to and within the metal shell li there is provided a sill block 15 supporting (see Fig. 5) the lambs 11 defining between them a door-way in alignment with the opening to-the heating chamber through which the muille enters and with the lintel slab 65. A door 19 slides vertically between the jamb pieces. Guides 8| supported through the spacers 83 from the front of the shell I are adapted to receive flanges of angles 85 secured to the sides of'the door to hold the latter in position and guide the same in its vertical movement. Herein the door I! is, as best seen in Fig. 5, shown as composed of three vertical bricks which are held together by through bolts 81 to retain them between the fore and aft extending flanges of the angles 85. As seen in Fig. 6. the bolt-receiving openings in these flanges are somewhat enlarged, thus permitting the adjustment of the body of the door relative to the guide flanges to position it properly in its openin E.

The door, being in direct alignment with the heating chamber and with the open end of the work-receiving mullle, is made substantially thicker than the Jamb pieces 11 adjacent the same and projects outwardly from the casing. Secured to shelf 89. The door closes on the sill l5 and the inner portion of the shelf, the door joint, as shown in Fig. 2, being preferably along a broken lijne. In Figs. 1 and 2 the door is shown slightly a ar.

It will be understood that the various blocks referred to are secured together by means of suitable refractory mortar or cement in accordance with the usual practices in masonry work.

I am aware that the invention may be embodied in other specific forms without departing from the spirit or essential attributes thereof, and I therefore desire the present embodiment to be considered in all respects as illustrative and not restrictive; reference being had to the appended claims rather than to the foregoing description to indicate the scope of the invention.

Iclaim: 1. An electric furnace of the class described comprising walls of refractory material defining an interior chamber, a door giving access thereto, opposed walls of the chamber having aligned openings, resistor rods the latter at the exterior is a load;

across the" chamber and having ends received in said openings, terminals engaging the ends of the rods and exposed beyond said walls for air cooling, and supplemental means retarding the transmission of heat extending outwardly from said walls between the terminals and in alignment with the chamber.

2. An electric furnace of the class described comprising walls of refractory material defining an interior chamber, a door giving access thereto, opposed walls of the chamber having aligned openings, resistor rods extending across the chamber and having ends received in said openings, terminals engaging the ends of the rods and exposed beyond said walls for air cooling, plates supported in spaced relation to said walls outward of the terminals and supplemental means retarding the passage of heat extending between said walls and plates in the space between the terminals.

3. An electric furnace comprising an enclosure having top, bottom, rear and side walls of refractory blocks, resistors extending between the side walls, a throat of refractory slab at the front having an opening, a muilie having a flanged front end forming a joint with the margins of said opening, a wall of brick exterior to said throat defining a door frame in alignment with the opening and a door in the frame.

4. An electric furnace comprising an enclosure having top, bottom, rear and side walls of refractory blocks, resistors extending between the side walls, a throat of refractory slab at the front comprising jambs and a separate lintel piece setting between the jambs and defining an opening, a wall of brick exterior to th'e throat comprising a sill and jambs at either side'of the opening and a door between the jambs adapted to cover said opening and lintel piece.

5. An electric furnace comprising an enclosure having top, bottom, rear and side walls of refractory blocks, resistors extending between the side walls, a throat of refractory slab at the front comprising jambs and a separate lintel piece setting between the lambs and defining an opening, a muflle having a flanged front end formin a Joint with the margins of the opening, a wall of brick exterior to the throat comprising a sill and jambs at either side of the opening and a door between the Jambs adapted to cover said opening and lintel piece.

6. An electric furnace of the class described comprising a metallic casing, an enclosure of refactory blockswithin the same comprising opposed walls having openings, resistor rods having ends received in said openings, the walls extending substantially to the casing adjacent said openings and exteriorly cut away about the same, heat insulating packing overlying the cut-away portions and a non-warping plate for the interior side wall of the casing overlying the said parts.

"I. An electric furnace of the class described comprising a metallic casing. an enclosure of refractory blocks within the same comprising opposed walls having openings, resistor rods having ends received in saidopenings, the walls extending substantially to the casing adjacent said openings and cut away between said locations to decomprising an enclosure of refractory "material defining an internal chamber, opposed walls having aligned, inwardly flaring openings, a centric group of resistor rods crossing the chamber at outer portions thereof having their ends extending into said openings nearly to the exterior of said walls, terminals extending slightly within the openings to engage the ends of the resistors and projecting in major part beyond said walls for air cooling, the outer surface of said walls being cut away to provide exterior elevatedheat-radiating portionsabout said openings and adjacent depressed portions and heat insulating material received in said depressed portions to minimize heat loss from the space within the group of resistors.

9. An electric furnace of. the class described comprising an enclosure of refractory material defining an internal chamber, opposed walls having aligned, inwardly flaring openings, a centric group of resistor rods crossing the chamber at outer portions thereof having their ends extending into said openingsnearly to the' exterior of said walls, terminals extending slightly within the openings to engage the ends of the resistors and projecting in major part beyond said walls for air cooling, the outersurface of said walls being cut away to provide exterior elevated heatradiating portions about said openings and adjacent depressed portions, heat insulating material received in said depressed portions to minimize heat loss from the space within the group of resistors and an additional heat-intercepting body supported exteriorly of said walls and within the group of said heat-radiating portions.

10. An electric furnace of the class described comprising walls of refractory material defining an interior chamber, a door giving access thereto, opposed walls of the chamber having groups of openings entering the chamber adjacent other walls thereof and being aligned in opposed walls, a non-conducting shield plate of relatively large dimension in two directions supported from each of said walls in exteriorly fixed spaced, substantially parallel relation thereto to overlie the group of openings therein and extend beyond the same, one of said plates having openings aligned with the wall openings, resistor rods adapted to be passed through the plate openings and wall openings to extend across the chamber with their ends received in the wall opening, terminals back-supported by the other plate engaging the adjacent ends of the rods, terminals engaging the opposite ends of the rods, and springs carried by the inner surface of said one plate and movable across said openings to engage the ends of the latter terminals for suspending the terminals and the interposed rods between and from the plates.

PERCIVAL B. cnocxanf 

